Backpack



FIG. 1 is a front perspective view of a backpack showing my new design;

FIG. 2 is a right side view of the backpack;

FIG. 3 is a left side view of the backpack;

FIG. 4 is a top view of the backpack;

FIG. 5 is a rear view of the backpack; and,

FIG. 6 is a bottom view of the backpack. 

The ornamental design for a backpack, as shown and described. 